Implantable pulse generator systems and other stimulation devices are used to treat chronic pain by providing electrical stimulation pulses from an electrode array placed epidurally near a patient's spine. Spinal cord stimulation (SCS) is a well accepted clinical method for reducing pain in certain populations of patients. SCS systems typically include an implantable pulse generator (IPG), lead wires and/or lead extensions, and electrodes connected to the lead wires.
The pulse generator generates electrical pulses that are delivered to the dorsal column fibers within the spinal cord through the electrodes which are implanted along the dura of the spinal cord. In a typical situation, the attached lead wires exit the spinal cord and are tunneled around the torso of the patient to a sub-cutaneous pocket where the pulse generator is implanted.
In order to protect the electronic circuitry from environmental conditions and/or other damage while the IPG is implanted within a patient, the IPG is frequently enclosed in a titanium case to provide protection and a hermetic, or completely sealed, environment. For example, the titanium case frequently includes two halves. Recesses are formed in each of the halves such that when the two halves are coupled together, holes are defined therein. Feedthrus extend through these holes to allow the lead wires or lead extensions to be electrically coupled to the electronic circuitry of the IPG. In some circumstances, it may be difficult to ensure that the assembly is hermetically sealed.
In particular, to properly establish the feedthrus, the titanium halves often must be aligned with respect to each other and with respect to the feedthru member. The assembly is then welded. The welded assembly is subsequently checked for leaks. If the resulting assembly is not hermetically sealed, the assembly is then reworked. Even if the assembly is sealed during formation, it may be possible for the feedthrus to later develop leaks. If the feedthrus do leak, resulting in the ingress of moisture, the IPG may fail prematurely, such as by damaging the electronic circuit of the IPG.
Moreover, the traditionally used titanium halves are difficult to properly weld such that a hermetically sealed case is produced. The traditionally shaped case is welded along a number of edges having varying profiles. Consequently, it is difficult to establish a constant welding speed and the work piece is rotated for proper weld orientation, often resulting in poor weld penetration. Additionally, because traditional cases butted mating pieces together and due to poor tolerances from manufacturing methods, little or no material was present under the welded seam, resulting in inferior welds.
Further, some designs allow the battery to be recharged using an external power source. The use of a highly conductive case may limit the rate with which the battery in an implanted medical device may be charged inductively through the skin. For example, commercially pure titanium, while relatively easy to machine, may be subject to induced heating of the case as a result of eddy currents caused during inductive charging.